Image reproducing device



Aug. 144.

P. T. FARNSWQRTH 'IMAGE REPRQDUCING DEVICE Filed June 20, 1942 FIG.I

WAVE

GEN ERATOR INVENTOR FARNSWORTH Patented Aug. 8, I944 AYES TENT IMAGE REPRODUCING DEVICE Application June 20, 1942, Serial No. 447,757

9 Claims. (Cl. 178-75) This invention relates to a projection tube and more particularly to a control arrangement in such a tube which employs the storage principle.

In projection tubes of this type, there is generally provided an unmodulated source of electrons. which electrons are controlled in accordance with stored electrical charges. These stored elec trical charges are developed by means of an electron beam which is modulated in accordance with received picture signals. In this way, the picture signals are effective in controlling the unmodulated source of electrons for an extended interval of time, such as the scanning line period or a field or frame period. The electrons controlled in this manner are utilized to produce a luminescent effect, the duration of which is obviously longer than the time interval allotted to the scanning of a single picture element. In this manner, a picture of increased brilliance is produced.

In conventional projection tubes of the type described, a charge image having the dimensions of the scanning line or of a complete picture is developed by means of a scanning beam modulated by picture signals. Obviously, a charge developed on an elemental area of the charge image must be neutralized before the scanning beam returns to this area to develop a new charge thereon after a line, field or frame interval. In some types of tubes in the prior art, the charges forming the charge image are permitted to leak away in accordance with an exponential function during the scanning period. Obviously, this is an inefiicient method of operation since the luminescence produced by the controlled electrons also decays according to an exponential function instead of maintaining its maximum value throughout the scanning period. Arrangements have been proposed in which this defect is supposed to be overcome by employing a second scanning beam which neutralizes the charges of the charge image shortly before new charges are created by the first scanning beam. Such arrangements, however, have generally been found to be diflicult to construct or to operate.

It is an object of the present invention, therefore, to provide a new and improved projection tube incorporating an electron control arrangement of simple construction and increased efficiency.

In accordance with the present invention, there is provided a cathode ray projection tube having a uniform source of electrons. A plurality of mutually insulated charge storage elements are ponally, a target means is provided and means for.

directing the controlled electrons from the uniform source onto the target means to produce a luminescent effect.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing,

Fig. 1 is a diagrammatic sectional view of a projection tube in accordance with the invention; and

Fig. 2 is a perspective view of a control arrangement embodying the invention and incorporated in the projection tube illustrated in Fig. 1.

Referring now more particularly to Fig. 1 of the drawing, there is shown a diagrammatic sectional view of a projection tube having an envelope comprising a main cylindrical portion H and a neck portion l2. At one end of the main cylindrical portion H, there is provided a linear cathode l3, preferably of the type that is indirectly heated, for producing a uniform source of electrons. The source of energy for making the cathode electron-emissive is provided by a battery M. The cathode I3 is positioned in a recess E6 of a supporting body ll, preferably of metal. Upon the supporting body I1, there is positioned a plurality of grid elements or wires l8 adjacent to each other. The grid elements I8 are insulated in a suitable manner from each other and from the supporting body I! and will be referred to in greater detail hereafter.

In the neck portion I2, there is provided an' electron gun for producing an unmodulated beam of electrons. The electron gun comprises a cathode 20, a control element or grid 22, and an accelerating anode 23. The cathode 20, the grid 22 and the anode 23 may be operated at progressively increasing potentials, as shown in in. The cathode 20 is energized by a battery 24 to a potential substantially below ground. The electron beam is focused by a magnetic focusing 'coil 25 of th conventional type, which is connected in series with a battery 26 and a variable resistor 21.

The electron beam is deflected across the charge storage elements I! by a pair of deflecting plates 28 energized by a generator 29 capable of producing a saw-tooth voltage of line or first frequency. In Fig. 1, this sweep would occur perpendicular to the face of the drawing.

A pair of metal members 3|, preferably L- shaped and conductively connected together, are positioned adjacent the portions of the elements I! which are impacted by the beam of electrons. From the terminal 32, a picture signal is fed through a blocking condenser 33, which is of negligible impedance to the frequencies involved; and the picture signal appears as potential variation at the members 3|, over the resistor 34. The members 3| constitute a collector for collecting secondary electrons emitted from the elements ill, in proportion to the strength of the picture signal.

The end of the main tube portion remote from the control elements I8 is provided with a target means 36. Preferably, the target means 36 is a layer of fluorescent material deposited on the inner vertical wall at the end of the main tube portion II. The electrons from the cathode l3, controlled by the charges on the elements I-l, are accelerated toward the target 36 by an electrode 31. Preferably, the electrode 31 is a coating on the interior of the main portion I of the envelope, as shown in Fig. 1, and is energized by a battery 38. A magnetic focusing coil 39, connected in series relationship with a battery 40 and a variable resistor 4| is provided in the conventional manner to focus the electron image of the controlled emission from the cathode l3 onto the target 36. Wher the cathode I3 is linear in form, as illustrated in the drawing, the electron image represents one scanning line. A pair of deflecting coils 42, which are fed by a scanning frequency generator 43, operating at a frame or second frequency, are provided for deflecting the electron image in a vertical direction across the target 36.

Fig. 2 shows a perspective view of the control arrangement described above. One method of building this control arrangement is to wind many turns of fine wire around the supporting body Preferably, several turns of the wire per unit cathode length correspond to a picture element. The wires are insulated from the supporting body H in a suitable manner. They are also insulated from each other by being separated from each other and being cut at the recess 44 in the body II.

In operation of the projection tube, a highvelocity electron beam is produced by the electron gun comprising the cathode 20, the control element 22 and the anode 23. The electron beam is of uniform intensity and is deflected across the elements l8 at line frequency to release secondary electrons therefrom. A portion of the secondary electrons is collected by the collector members 3| in accordance with the instantaneous potential thereof which is controlled by the picture signals applied thereto, as described above. As is well known, an insulated member which is bombarded by high-velocity electrons and emits secondary electrons tends to approach the potential of an adjacent collector of the secondary electrons. In this manner, the number of secondary electrons emitted by the successive elements l8 under bombardment of the scanning beam varies in accordance with the picture signals applied to the collector members 3| and,

hence, a charge image corresponding to a single scanning line is produced on the elements |l which controls the emission from the linear cathode |3. Once, one of the grid elements "has acquired a certain charge and potential, it retains the same over a. relatively long period of time since it is perfectly insulated from the supporting body II. The potential is not appreciably influenced during the rest of the line scanning cycle by subsequent changes in the potential of the collector members 3|. Obviously, therefore, the control effect of the elements I! and the luminescence produced by the electrons from the cathode |3 remain constant until the scanning beam is ready to scan the control elements again. During the re-scanning, the potential of the collector is varied by the picture signals from its previous value. Thus, new charges and new control potentials are established on the same control element during each cycle of line scanning.

During the scanning of the elements It by the electron beam, the deflecting fleld generated by the coils 42 changes continually to place successive luminescent lines of an image on the target 38. I

It will be apparent from the above description that such operation greatly increases the elliciency of a projection tube while still providing a simple construction thereof.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A cathode ray projection tube having a uniform source of electrons, a plurality of mutually insulated charge storage elements positioned adjacent said uniform source of electrons for controlling the emission of electrons therefrom in accordance with the individual charges on said elements, means for producing an unmodulated beam of electrons, means for deflecting said beam across said elements to liberate secondary electrons therefrom to produce charges thereon, a collector for collecting said secondary electrons, means for varying the potential of said collector in accordance with pic ture signals, thereby to control the charges on said elements, a luminescent target means, and means for directing the electrons from said uniform source onto said target means to produce a luminescent effect.

2. A cathode ray projection tube having a uniform source of electrons, a plurality of mutually insulated charge storage elements positioned adjacent said uniform source of electrons for controlling the emission of electrons therefrom in accordance with the individual charges on said elements, means for producing an unmodulated beam of electrons, means for deflecting said beam across said elements to liberate secondary electrons therefrom to produce charges thereon, a collector for collecting said secondary electrons, means for varying the potential of said collector in accordance with icture signals, thereby to control the charges on said elements, a luminescent target means, means for directing the electrons from said uniform source onto said target means, and means for deflecting the electrons from said uniform source across said target means to produce a luminescent effect.

3. A cathode ray projection tube having a uniform source of electrons, a plurality of mutually insulated charge storage elements positioned adjacent said uniform source of electrons for controlling the emission of electrons therefrom in accordance with the individual charges on said elements, means for producing an unmodulated beam of electrons, means for deflecting at a first frequency said beam across said storage elements to liberate secondary electrons therefrom to produce charges thereon, a collector for collecting said secondary electrons, means for varying the potential of said collector in accordance with picture signals, thereby to control the charges on said elements, a luminescent target means, means for directing the electrons from said uniform source onto said target means, and means for deflecting at a second frequency the electrons from said uniform source across said target means to produce a picture.

4. A cathode ray projection tube having a linear cathode for producing a uniform source of electrons, a plurality of mutually insulated charge storage elements positioned adjacent said linear cathode for controlling the emission of electrons therefrom in accordance with the individual charges on said elements, means for producing an unmodulated beam of electrons, means for deflecting said beam across said storage elements to liberate secondary electrons therefrom to produce a linear charge pattern thereon, a collector for collecting said secondary electrons, means for varying the potential of said collector in accordance with picture signals,

thereby to control the charges on said elements, a luminescent target means, meansfor directing the electrons from said uniform source ontosaid target means, and means for deflecting the electrons from said linear cathode across said target means to produce a picture.

5. A cathode ray projection tube having a uniform source of electrons, a plurality of mutually insulated charge storage elements positioned ad- 6. A cathode ray projection tube having a uniform sourceof electrons, a plurality of mutually insulated charge storage elements positioned adiacent said uniform source of electrons for controlling the electrons therefrom in accordance with the charge on said elements, means for ,pro-

ducing an unmodulated beam of electrons, means for deflecting said beam across said elements to liberate secondary electrons therefrom to produce charges thereon, a pair of angularly shaped electrodes for collecting said secondary electrons, means for varying the potential of said electrodes in accordance with picture signals, a luminescent target means, and means for directing electrons from sai d uniform source onto said target means to produce a luminescent eflect.

jacent said uniform source of electrons for controlling the electrons therefrom in accordance with the charge on said elements, an electron gun for producing an unmodulated beam of electrons, means for deflecting said beam across said elements to liberate secondary electrons therefrom to produce charges thereon, a collector for collecting said secondary electrons, means for varying the potential of said collector in accordance with picture signals, a luminescent target means, and means for directing electrons from said uniform source onto said target means to produce a luminescent effect.

7. A cathode ray projection tube having a uniform source of electrons, a plurality of mutually insulated charge storage elements positioned adjacent said uniform source of electrons for controlling the emission of electrons therefrom in accordance with the individual'charges on said elements, means for producing an unmodulated beam of electrons, means for directing said beam of electrons in a first direction toward said elements, means for deflecting said beam across said elements to liberate secondary electrons therefrom to produce charges thereon, a collector for collecting said secondary electrons, means for vary i ngrthe potential of said collector in accordanfe with picture signals, thereby to control the charges on said elements, a luminescent target means, and means for directing electrons from said uniform source in a second direction onto said target means to produce a luminescent effect.

8. The method of producing an image on a recording surface which comprises the steps of producing a uniform stream of electrons, controlling said stream of electrons by a charge image in the path of said stream of electrons, utilizing an unmodulated beam of electrons to liberate secondary electrons, collecting liberated secondary electrons in accordance with image signals to vary said charge image, and directing said controlled stream of electrons onto said recording surface for producing a luminescent efiect thereon.

9. The method of producing an image on a recording surface which comprises the steps of producing a linear uniform stream of electrons, controlling said stream of electrons by a charge image in the path of said stream of electrons, producing an unmodulated beam of electrons, defleeting said beam of electrons to liberate secondary electrons, collecting said secondary electrons in accordance with image signals to vary the said charge image, and deflecting said controlled stream of electrons with respect to said recording surface for producing a picture thereon.

PHILO 'r. FARNSWORTH. 

